The present invention is directed to bicycle sprocket assemblies and, more particularly, to a bicycle sprocket assembly that has a chain support structure.
A bicycle sprocket assembly may comprise, for example, a plurality of chain-engaging sprockets attached to a freewheel assembly mounted together with a rear wheel hub. The smallest-diameter sprocket having the least number of teeth usually is positioned on the axially outermost side, and the largest-diameter sprocket having the greatest number of teeth is positioned on the axially innermost side. A rear derailleur typically is mounted in close proximity to the sprocket assembly for switching a bicycle chain among the plurality of sprockets.
In such a sprocket assembly, the largest-diameter sprocket is mounted close to the spokes of the rear wheel. If the chain accidentally derails axially inwardly from the largest-diameter sprocket and drops toward the rear wheel hub, a nearby spoke may be damaged. Conventional approaches to solve this problem include mounting a disc-shaped spoke protector between the largest-diameter sprocket and the spokes to reduce the risk of the chain derailing from the sprocket and to reduce the risk of damage to the spokes if the chain does derail from the sprocket. The spoke protector usually is made of a transparent resin, and the spoke protector is formed with a diameter far greater than the diameter of the largest-diameter sprocket. See, for example, spoke protector model number CS-LG50 shown at pages 48-49 of the 2006 Bicycle Components Trade Sales & Support Manual, August 2005, published by Shimano Inc. Unfortunately, the spoke protector increases the number of parts that must be assembled to form the wheel assembly. The spoke protector also increases the cost of the wheel assembly.